1. Field of the Invention
The present invention relates to a compressor, and more specifically to a compressor used in a refrigeration circuit of an air-conditioning system for a vehicle.
2. Description of the Related Art
The compressor of a refrigeration circuit of this type includes a housing in which a suction chamber and a discharge chamber are defined, and a compression unit accommodated in the housing. The compression unit repeatedly performs a series of processes, which include the suction of a refrigerant as a working fluid, the compression of the sucked refrigerant, and the discharge of the compressed refrigerant into the discharge chamber. The high-pressure refrigerant in the discharge chamber is delivered from the discharge port of the housing toward a condenser of the refrigeration circuit. The delivered refrigerant flows through the refrigeration circuit and is returned into the suction chamber through the suction port of the housing. In short, the refrigerant circulates through the refrigeration circuit.
The refrigerant contains mist-like lubricating oil. The lubricating oil contained in the refrigerant not only lubricates sliding surfaces, bearings, and the like, in the compressor but also is useful for sealing compression chambers defined in the compression unit.
However, when a great deal of lubricating oil is contained in the refrigerant flowing through the refrigeration circuit except for the compressor, the lubricating oil deteriorates the refrigeration performance of the refrigeration circuit, namely the air-conditioning system. Therefore, the compressor disclosed in Unexamined Japanese Patent Publication No. 2001-295767 is provided with an oil separator, which is disposed in a discharge chamber.
The oil separator includes a separating chamber located adjacently to the discharge chamber. The separating chamber communicates with the discharge chamber through jet holes and has a separating tube that is concentrically arranged therewithin. The refrigerant in the discharge chamber flows through the jet holes into the separating chamber and swirls around the separating tube. Such a swirling movement of the refrigerant applies a centrifugal force to the lubricating oil contained in the refrigerant, thereby separating a portion of the lubricating oil from the refrigerant. After running into the inner surface of the separating chamber, the separated lubricating oil flows downward along the inner surface of the separating chamber, and is collected from the separating chamber to be reserved in an oil chamber. The refrigerant that has undergone the action of centrifugal separation is guided from the separating chamber through the separating tube to the discharge port.
The lubricating oil in the oil chamber is sprayed into the suction chamber through an orifice path and is mixed again into the refrigerant in the suction chamber.
When the oil separator is built in the compressor, the refrigerant flowing through the refrigeration circuit except for the compressor contains a small amount of lubricating oil. The oil separator then prevents a deterioration in refrigeration performance of the air-conditioning system, which is caused by the lubricating oil.
As is already apparent from the above explanation, the oil separator uses centrifugal separation to separate the lubricating oil from the refrigerant. For an effective separation of the lubricating oil, therefore, the refrigerant needs to be powerfully swirled around the separating tube at high speed.
However, when the compressor is operated in a low speed range, that is, when a delivered amount of the refrigerant from the compressor is small, the amount and flow rate of the refrigerant that flows from the discharge chamber into the separating chamber are both lessened. As a result, it is impossible to produce a high-speed and powerful swirling flow of the refrigerant around the separating tube.
Accordingly, in a case that the compressor is in the aforementioned operational condition, the oil separator cannot satisfactorily separate the lubricating oil from the refrigerant. This causes not only a deterioration in refrigeration performance of the air-conditioning system but also a reduction in stores of the lubricating oil in the oil chamber, which makes the liquid level of the lubricating oil lower than the orifice path.
In such a case, the orifice path is not filled with the lubricating oil, so that the refrigerant in the discharge chamber short-cuttingly flows through the separating chamber, the oil chamber and the orifice path into the suction chamber. This considerably decreases the compression efficiency of the compressor, that is, refrigeration performance of the air-conditioning system.